Admissions related to interstitial cystitis in Japan: an estimation based on the Japanese diagnosis procedure combination database.

We estimated the incidence of admissions related to interstitial cystitis in Japan using a national administrative claims database, the Diagnosis Procedure Combination database, which included information for 53.6% of urological training hospitals certified by the Japanese Urological Association. "Admissions related to interstitial cystitis" was defined as those cases whose ICD-10 code for the main reason for admission was N301 (interstitial cystitis) between 2007 and 2009. Among 8.42 million inpatient cases, 784 female and 212 male patients with interstitial cystitis were identified. The ratio of females to males was 3.69 and the median age was 67 years (range 5-92 years). The admission incidence (per 100 000 person-years) in females and males was estimated to be 1.35 (95% confidence interval 1.25-1.46) and 0.37 (0.31-0.42), respectively. This incidence is low compared with other reports. Possible reasons for this finding include racial difference, clinical examination methods, lack of outpatient data and poor health-care coverage of interstitial cystitis.